Portable liquid oxygen storage-gas supply units are small light weight devices which comprise a liquid oxygen storage container with associated systems to dispense the liquid oxygen as breathing oxygen for use by a person handicapped, for example, by pulmonary or cardiac disorders. These units provide the handicapped individual with improved mobility in comparison with large stationary oxygen supply devices.
Because these units are intended for use by the handicapped, it is especially important that they be light weight and compact, simple to use, reliable, and safe with the observance of only minimal precautions.
The requirement that the unit be light weight and compact results in the designed liquid oxygen storage capacity being small, for example, about 1 to 2 pounds of liquid oxygen. The unit must therefore be capable of being easily and safely refilled by the handicapped person in his home from a large stationary liquid oxygen supply source.
To provide maximum mobility away from a stationary oxygen source, it is necessary that the portable unit to be filled to design capacity with liquid oxygen. To insure safety, it is important that the unit be reliably filled to the capacity which the handicapped person expects to have available in order to preclude the premature exhaustion of the oxygen supply when the user is away from a stationary oxygen source.
Accordingly, the prior art has developed automatic fill termination systems in order to provide for the reliable refilling of portable oxygen supply units to design capacity and to prevent overfilling of the unit which could result in spillage of liquid oxygen with the attendant safety hazards such as frost bite of persons contacted and increased danger of fire and explosion. Such automatic systems minimize the operational participation of the handicapped person or other individual refilling the unit in the home and increase the reliability, simplicity and safety of the refill.
The art has thus sought to increase the reliability of such automatic fill termination systems. Furthermore, the art has sought to achieve structurally simple designs for such portable oxygen supply units which both decrease the unit's weight and increase the unit's reliability during refill and breathing use.
Portable liquid oxygen storage-supply units comprise a small evacuable double-walled insulated container suitable for storage of a cryogenic liquid. Typically, a first conduit penetrates the upper head of the container vessel and extends to near the bottom end of the vessel. Stored liquid oxygen is withdrawn through this conduit and through an associated vaporizer and control circuit to supply warm gas to the user for breathing purposes. A second conduit penetrates the upper head of the container vessel and terminates near the top of the unit for the purpose of venting excess pressure from the vessel as needed.
If the portable unit is filled in its upright position, the liquid withdrawal or dispensing conduit can function as a liquid fill conduit. Similarly, the vent conduit retains its venting functions.
The prior art has also developed inverted fill methods for portable oxygen storage-supply units. In this method, the portable unit is inverted to a top-down-bottom-up position over a large stationary liquid oxygen container for performing the fill. This results in an advantageous shorter connecting conduit between the two containers when the fill is taking place.
When an inverted fill method is used, the portable unit's excess presssure gas vent conduit functions as a liquid fill conduit and the breathing use liquid withdrawal conduit functions as a gas vent conduit.
Portable liquid oxygen storage-dispensing units which are invertible between a top-up dispensing and bottom-up filling positions are described in U.S. Pat. Nos. 3,797,262 and 3,864,928 to Eigenbrod. These patents likewise disclose automatic fill termination systems used to terminate the refilling of the portable unit.
Copending U.S. Patent Application Ser. No. 125,889 filed Feb. 29, 1980 discloses an improved automatic fill termination apparatus which may be advantageously incorporated with a portable liquid oxygen storage-supply unit intended for using the inverted fill method.
The automatic fill termination system of copending Application Ser. No. 125,889, the entire disclosure of which is incorporated herein by reference, utilizes a quick-closing plug type valve which is mounted in an uninsulated conduit circuit external to the portable unit's liquid oxygen storage container which is in fluid communication with the container's liquid withdrawal conduit. When inverted fill is taking place by liquid oxygen entering through the excess pressure gas vent conduit, gas is vented through the liquid withdrawal conduit, the external conduit circuit and through the quick-closing plug type valve to atmosphere. The quick-closing plug type valve is designed to close and terminate fill upon slight increases in pressure of the venting vapor. Thus, when the portable container becomes full, liquid oxygen will enter the liquid withdrawal conduit and flow toward the external uninsulated conduit circuit and vaporize whereupon the quickly-closing plug type valve promptly and dependably closes and terminates the fill thereby providing precise control and avoiding overfill.
Automatic fill termination systems for portable liquid oxygen storage-dispensing units therefore typically terminate the fill of the unit upon the sensing of the presence of liquid oxgen caused by the overflow of liquid oxygen from the filled container into the conduit circuit venting gas during the fill. Thus, liquid oxygen entrained with the venting gas during the fill could prematurely cause the fill termination effect intended to occur when the container is full and liquid oxygen is just about to commence overflow through the vent circuit.
If entrained liquid oxygen in the venting gas does not cause premature termination of the fill, its presence will still result in excessive cooling of the conduit circuit venting gas during the fill and the means for sensing the presence of liquid oxygen in this circuit and therefore may result in a decrease in the sensitivity of the automatic fill termination system being used. In either event, the reliable, precise control to insure a complete fill but avoid an overfill is being impaired.
Finally, entrained liquid oxygen in the venting gas during the fill operation leads to undesirable transfer losses.
As hereinbefore discussed, a portable liquid oxygen storage-supply unit intended to be replenished with liquid oxygen by the inverted fill method includes two conduits which penetrate the top of the storage-dispensing evacuable double-walled container when it is in its upright normal breathing use orientation. A first conduit extends to near the bottom of the container (when in upright orientation) and serves the dual function of a liquid withdrawal conduit when the container is positioned in its top-up breathing oxygen dispensing mode and as a gas vent conduit when the container is positioned in its inverted bottom-up liquid oxygen filling mode. This first conduit may be referred to as a liquid withdrawal-gas vent conduit. A second conduit terminates near the top of the container (when in upright orientation) and serves the dual function as an excess pressure gas vent conduit when the container is positioned in its top-up breathing oxygen dispensing mode and as a liquid fill conduit when the container is positioned in its inverted bottom-up liquid oxygen filling mode. This second conduit may be referred to as a gas vent-liquid fill conduit.
Since the portable liquid oxygen storage-dispensing container is an evacuable double-walled container constructed to provide a vacuum insulation space between the two walls, it is desirable to provide for a single conduit penetration to minimize construction seals which have the potential for leakage. The prior art has placed the two dual function conduits side by side passing through a single opening essentially along the axial center line of the container in conjunction with suitable support and plugging arrangements. Alternately, the prior art has used a relatively complex manifold arrangement at the inner side of the container penetration to provide for the fluid path of the two dual purpose conduits into the container storage space.
A need, therefore, exists for an invertible liquid oxygen storage-dispensing container wherein the liquid withdrawal-gas vent conduit and the gas vent-liquid fill conduit are arranged for a structurally simple penetration of the top end of the double-walled container and a structurally simple termination of the respective conduits in their appropriate locations within the storage container which arrangement also provides for liquid oxygen fill of the container in its inverted position without excess entrainment of liquid oxygen in the venting gas during the container fill.